Carbon Dioxide Flux From Soils in Switchgrass Production.

Increasing national and international concerns regarding climate change, and the push to meet the goal of replacing 30% of fossil fuels with biofuels by 2030 has created an increasing need for research relevant to the environmental implications of growing bioenergy crops. The main objective of this study was to measure annual, seasonal, and daily soil CO₂ flux from switchgrass produced for biofuel feedstock. Measurements were taken hourly from June 1, 2010 to August 18, 2011using an automated soil CO₂ flux measurement system. As previously reported, soil temperature and moisture had a significant influence on CO₂ flux. Soil temperature and soil moisture were able to explain 83% of variance in flux. The summer months exhibited the highest flux rate followed by spring, fall, and winter due to the favorable conditions for microbial metabolism in the warm summer months. Although largely overlooked in previous research, the winter months (mid Dec to mid Mar) did contribute 5.4 Mg CO₂ ha^-1 season^-1 (±2.5 Mg CO₂ ha^-1 season^-1) from clumps (cover) and 4.0 Mg CO₂ ha^-1 season^-1 (±3.2 Mg CO₂ ha^-1 season^-1) from between clumps (bare). Total annual CO₂ flux on the study plot was determined to be 7.4 Mg CO₂ ha^-1 (±4.08 Mg CO₂ ha^-1). Our Soil CO₂ data coupled with below ground carbon data will enhance our understanding on soil carbon dynamics under bioenergy crop production.